Tantalum base alloys



July 2, 1968 R. L. AMMON ETAL 3,390,983

TANTALUM BASE ALLOYS Filed April 20, 1964 0 l4 W/O TOTAL ALLOY ADDITION:1 ---IO 'W/O TOTAL ALLOY ADDITION u O: D Y E m 200 41' E DUCTILE 5 RT h5 o .2. (I, Z 4 5-200 {l4 BRITTLE (21') BRITTLE we I l o 2 a 4 5 e 1TUNGSTEN-HAFNIUM mmo WITNESSES: INVENTORS Robert L. Ammon 0nd Righurd T.Begley United States Patent 3.390983 TANTALUM BASE ALLOYS Robert L.Ammon, Baldwin, and Richard T. Begiey, Penn Hills, Pa., assignors toWestinghouse Electric Corporation, East Pittsburgh, Pa., a corporationof Pennsylvania Fiied Apr. 20, 1964, Ser. No. 361,175 9 Claims. (Cl.75-174) The present invention relates to tantalum base alloys which aresuitable for use in applications wherein high strength at elevatedtemperatures is required or wherein ductility at sub-zero temperatures,or wherein both characteristics are required. More particularly, theinvention relates to alloys of the character described which are inaddition readily fabricable and weldable.

Fabricable and weldable alloys possessing strength and oxidationresistance at elevated temperatures have many industrial, military, andaerospace applications. Obviously, advances in many areas of technologyare dependent upon or closely related to the availability of alloyspossessing these properties. For example, the development of improvedrocket nozzles and of improved blades for gas turbines is attendant uponthe development of improvement of such alloys.

A number of tantalum base alloys have been developed prior to thepresent invention. Nearly all of these alloys, however, exhibit poorwelding or fabricability properties or have only moderate hightemperature strength, and in some cases suffer from both of theseshortcomings.

The present invention is an improvement upon the alloys disclosed in US.application Ser. No. 208,617,- filed July 9, 1962, now Patent No.3,166,414.

In accordance with the present invention, it has been found thatfabricable and weldable alloys possessing strength at temperatures above2000 F. and exhibiting sub-zero temperature ductility can be produced byalloying tantalum, tungsten, and hafnium in specified proportionstogether with minor amounts of one or more interstitial elements.

In view of the foregoing, it is an object of the invention to provideworkable alloys which possess strength at elevated temperatures andwhich exhibit good sub-zero temperature ductility, comprisingpredetermined proportions of tungsten and hafnium with one or moreinterstitial elements and the balance being tantalum, with incidentalamounts of impurities.

Another object of the invention is the provision of tantalum base alloysto which the hafnium and tungsten are added in a predetermined ratio byweight so as to produce the maximum sub-zero ductility.

Other objects, features and advantages of the invention will beelaborated upon during the forthcoming description of illustrativeembodiments thereof, when taken in conjunction with the accompanyingdrawing, wherein:

The figure is a graphical representation illustrating the effects ofvarying the ratio by weight of the tungsten and hafnium additions to thealloy.

Tests for ductility of a metal sheet are commonly made by bending thesheet about a mandrel having a radius of four times the sheet thickness,the sheet being bent about 90 around the mandrel, both being cooled to agiven temperature and noting if any rupture or crack appears on themetal sheet. This test is defined by the 4T bend test. For some cases,an application of the same test is applied by employing a mandrel whoseradius is twice that of the sheet thickness, and this is known as the 2Tice bend test. Welded areas in the bending zones successfully subjectedto such tests are an indication of good weld ductility. Cracks or breaksin the bent sheet indicate lack of sufiicient ductility at the testtemperature.

In accordance with the present invention, ternary tantalum base alloysare produced comprising from 8 to 11% tungsten, from 1.5 to 3% by weighthafnium, the total being from 10% to 14%, carbon up to 0.05%, nitrogenup to 0.07%, oxygen up to 0.07% and the balance being tantalum, with theratio by weight of tungsten to hafnium being in the range of 3:1 to 5:1and preferably about 4:1 for sheets meeting the 2T test, and 2.521 to5.5:1 for the 4T test. Incidental amounts of impurities and othermetallic additives to a total of up to 1% of a maximum may be present.Contemplated by the invention are the ternary tantalum base alloyshaving the aforementioned ranges of tungsten and hafnium together withminor amounts of interstitial elements comprising carbon in an amount ofat least 0.005% and nitrogen in an amount of at least 0.005%. t

The alloy may be melted by one of several procedures which will insurehomogeneity and a minimum of contamination. For example, unalloyed, highpurity, tantalum together with the proper amounts of pure tungsten andhafnium can be fed into a conventional non-consumable arc meltingfurnace containing an inert atmosphere such as argon or in a furnace inwhich a vacuum can be maintained. Desirably, the resulting ingot shouldbe remelted several times, for example by non-consumably arc-melting itusing a tungsten electrode to achieve the requisite homogeneity; andthen may be hot worked to the desired shape. The alloy can also beprepared by levitation melting of a ball or rod compressed from wire,pellets or powders of components of the alloy, using induction heatingtechniques. Electron beam melting and consumable arc melting of thealloys are also satisfactory techniques.

Referring now to FIG. 1 of the drawing, the graphical representationtherein illustrates the unique sub-zero characteristics of the alloysproduced in accordance with this invention. In FIG. 1, variations intungsten-hafnium ratio of the alloys are plotted against the respectivetransition temperature in degrees Fahrenheit. The curves 10 and 12respectively represent the result of weld bend tests for the 2T and the4T conditions. Data for the curves 10 and 12 are obtained from fouralloy compositions each of which contains a total of 14 weight percentof combined tungsten-hafnium additions. 0n the other hand, the singlepoint 14 represents an alloy having a combined total of 10 weightpercent of tungsten-hafnium addition. The same test curve values areobtained when the alloys contain carbon up to 0.04%, nitrogen up to0.02% and oxygen up to 0.02%. At 0.05% carbon the 4T test for the 8%tungsten 2% hafnium alloy results in a 200 F. transition temperature.

An inspection of FIG. 1 indicates that the ductility, as represented bythe respective transition temperatures, exhibits a pronounced maximumeffect at a tungsten to hafnium ratio of approximately 4:1. Thecorresponding brittle and ductile areas of the graph are indicatedthereon, the brittle area being below the respective curves. For manyapplications involving sub-zero conditions, as evidenced from the graph,tungsten to hafnium ratios of between 3:1 and 5:1 can be produced andutilized advantageously, particularly for the 4T condition. For lessrigorous cold conditions a ratio in the range of 2.5:1 to :1 issuitable.

The compositions of the alloys utilized for the prep- The alloys ofTables I and II are markedly improved aration of FIG. 1 are shown in thefollowing Table I: by adding carbon, nitrogen and oxygen as interstitialTABLE I.TENSILE PROPERTIES OF TA-W-HF ALLOYS Tungsten to Ultimate YieldHeat Hainium Temperature Tensile Strength Elongation Remarks Ratio F.)Strength 0.2% Offset (Percent) (K s.i.) (K s.i.)

Ta-8W2Hf 4:1 320 147. 5 131.0 31 Material reduced recrystallized 75 84.0 68. 6 31 1 hr. at 3,000 13. 2, 400 38.0 26. 4 29 3,000 15. 6 14.5 31

Ta-8W-6Hi 1. 33:1 -320 172. 0 157.0 25 Material reduced 80%;recrystallized 75 106. 8 06. 2 32 1 hr. at 3,000 F. 2, 400 52.3 39. 7 233,000 20.0 18.6 81

Ta-10W-4Ht 2. :1 320 172. 0 163.8 23 Material reduced 80%;recrystallized 75 106. 0 97. 2 26 1 hr. at 3,000 F. 2, 400 49. 6 37.0 323,000 25.8 25. 3 67 Ta-11,2W-2.8Hf 4:1 320 Material reduced 70%;recrystallized 75 104.3 97. 6 *14 1 hr. at 3,000 F. 2, 400 42. 2 29. 331 3, 000 20. 1 20. 1 38 Ta-12W-2Hf 6:1 320 172. 5 159. 0 29 Materialreduced 80%, recrystallized 75 105. 4 06. 8 32 1 hr. at 3,000 F. 2, 40056. 3 40. 0 36 3, 000 24. 2 23. 3 57 *Equipment maltunctioned. Teststopped after ultimate was reached. K s.c.=Thousa11ds of pounds persquare inch. Strain rate 0.005 in./in./1m'n. at low temperatures. Strainrate 0.05 in./in./mi11. at high temperatures.

Table I also lists the tensile properties of the alloys components, inamounts not exceeding 0.05% carbon, shown graphically in FIG. 1. Thedata of Table I shows 0.07% oxygen and 0.07% nitrogen. the significantimprovement in tensile properties when 30 The advantageous addition of aminor amount of an the total tungsten and hafnium concentration israised interstitial element such as carbon is illustrated by the from to14 weight percent. The alloys represented by following Table III:

TABLE III.COHPARATIVE TENSILE PROPERTIES Tenzpelrafure Ultimate YieldStrength Elongation Total Tung- Alloy Strength 0.2% Oflset (percent)stenHa[nium (K s.i.) (K s.i.) Solute (w/o) Tit-SW-Zllf 320 147. 5 131. 031 10 Ta-9.GW-2.4HI0.01C 320 184. 6 175.0 28 12 Strain Rate 0.005in./in./1nin. at low temperatures. Strain Rate 0.05 in./in./min. at hightemperatures.

Table I have been found to exhibit excellent fabricability,

elevated temperature strength and in those alloys having a In theforegoing table, the tensile properties of the tungsten to hafnium ratioof between 3:1 and 5:1, excelalloy Ta-9.6W-2.4Hf-0.01C is compared withone of the lent weldability. Additionally, it has been found thattanalloys, Ta-SW-ZHf, which is plotted in FIG. 1 and listed talum basealloys containing up to 14 weight percent in the preceding Tables I andII. For the alloy Ta-8W- additions of tungsten-hafnium in ratios rangingfrom 2.511 2Hf, the same data are used in Table III as in Table I, to5.5 :1 have been melted and processed to sheet without save that datafor the temperature condition 3500 F. difliculty. are added. By crossreferring to Tables I, II and III, the The following Table II lists theone and ten hour stress alloy Ta-9.6W-2.4Hf-0.01C can also be comparedas to rupture properties of the various tantalum ternary alloys tensileproperties with the other alloys described herein at 2400 F., inaccordance with the invention: for the temperature range 320 to 3000 F.

TABLE II Stress for Stress for Tungsten- Total Solute Heat N0. 1 hourlife 10 hour life Hainium (w/o) (K s.i.) (K s.i.) Ratio 'IBM-2,Ta8W-6Hi- 35. 3 25. 3 1. 33:1 14 TBu-a, Pa-10W-4Hf- 36. 5 2s. 0 2. .5114 TBM-14, Ta11.2W-2.8Hf. 39. 0 32. 5 4; 1 14 TBM-4, Ta12W-2Hf 38.0 29.56:1 14 T111,Ta8W-2Hf 33.5 20.0 4:1 10

Table II exemplifies the improved stress rupture properties of thetantalum alloys of the invention as the total The addition of theinterstitial element, carbon, pro- Weight percentage of thetungsten-hafnium solute is induces a significant improvement in tensileproperties as creased from 10% to 14%. Table II also indicates thatcompared to the other alloys noted herein, and partiularly theaforementioned stress rupture properties are optimized to Ta-8W-2Hf. Atthe same time, the sub-zero ductility with tungsten-hafnium ratios inthe neighborhood of 3:1 of the alloy Ta-9.6W-2.4Hf-0.01C is improved byutilizing to 5 :1. an intermediate total solute addition of 12%.

TABLE IV.STRESS RUPTURE PROPERTIES Alloy Stress For One Stress For 10Hour Liie (K s.i.) Hours Life (K s.i.

Ta-BW-2Hi 33. 5 26. Ta-9.6W2.5, Iii-0.010 44.0 35.0

By cross referring to Tables II and IV, the Ta-9.6W- 2.5Hf-0.01C alloyof the invention can likewise be compared as to comparative stressrupture properties with the other tantalum alloys disclosed herein. Itis seen that the tantalum alloy Ta-9.6W-2.4Hf-0.01C exhibits a markedimprovement over the alloy Ta-SW-ZI-If and significant improvement instress rupture properties over the remaining alloys. The effect of thecarbon addition upon tensile and stress rupture properties isparticularly significant when comparing the alloy Ta-9.6W-2.4Hf-0.01Cwith the alloy Ta-8W-2I-If and Ta-11.2W-2.8Hf, all three alloys have a4:1 tungsten to hafinum ratio, but the latter two alloys havingcorrespondingly lesser and greater total solute additions than the firstalloy.

The last disclosed tantalum alloy, Ta-9.6W-2.4Hf- 0.01C, is readilyfabricable; for example, it can be fabricated to sheet from three inchdiameter are cast ingots without difficulty. In addition to the improvedelevated temperature properties and stress rupture properties, thisalloy, as in the case of the other alloys disclosed herein possessesexcellent sub-zero weld bend ductility. This alloy is completelyductile, for example, over 2.5T at 250" F. for both stress-relieved andrecrystallized base metal.

Accordingly, the present invention comprises broadly, the ternarytantalum-tungsten-hafnium alloy comprising a total W-Hf solute additionin the prescribed range of 10% to 14% and with the tungsten to hafniumbeing in the preferred ratio range of between 3:1 and :1; wherein thealloys include with small additions of carbon, nitrogen and oxygen asinterstitial components.

In the course of investigating tantalum base alloys containing tungstenand hafnium, alloys with a nominal composition of Ta-8W-2Hf togetherwith individual additions of up to 0.05 w./o. carbon, 0.07 w./o. oxygen,0.07 w./o. nitrogen and with multiple additions of up to 0.01 w./o. ofeach interstitial element carbon, oxygen and nitrogen have been found topossess desirable qualities of fabricability, weldability, andattractive high temperature properties. These tantalum base alloyscontaining the aforementioned concentrations of interstitial elements,respectively, can be processed to sheet from are cast ingots withoutdifiiculty. Additionally, sheet material of the aforementioned alloyscan be welded without difficulty.

The efiect of various interstitial additions on the weld bend transitiontemperature for the 2T and 4T bend conditions is illustrated in thefollowing table:

TABLE V.-WELD BEND DUCTILITY 0F INTERSTITIAL- CONTAINING TANTALUM ALLOYSFrom the foregoing Table V, it will be seen that all of the interstitialalloys noted therein exhibit weld bend ductility at 320 F. with theexception of the alloy containing 0.5 w./o. carbon. The weld bendtransition for this alloy was raised to room temperature for the 2Tcondition and to 200 F. for the 4T condition.

The tensile properties of the tantalum interstitial containing alloysare shown in the following table:

TABLE VI.LOW AND HIGH TEMPERATURE TENSILE PROPERTIES OFINTERSTITIAL-CONTAINING T-111 ALLOYS Ultimate Yield Heat No. TemperatureTensile Strength Elongation Remarks F.) Strength 02% Offset (percent) (Ks.i.) (K s.i.) TBM-lO, T111+0.02C 230 171. 2 153.8 23 Material reduced70%; recrystallized 75 108. 7 98. 75 26 1 hr. at 3,000 F. 2, 400 53. 735. 7 34 3, 000 20. 4 19. 7 78 TBM-le, T111+0.05C 320 170. 4 148.6 26Material reduced 68%; recrystallized 75 108. 7 82. 4 29 1 hr. at 3,000F. 2, 400 54. 0 35. 3 23 3, 000 21. 4 21.4 68 TBM-ll, T111+0.02C 320148. 25 137. 8 33 Material reduced 70%; recrystallized 75 88.8 78. 7 321 hr. at 3,000 F. 2,400 41. 7 25. 8 38 3, 000 15. 6 14. 9 52 TBM-17,T-111+0.05C 320 152. 7 140. 3 34 Material reduced 68%; recrystallized 7588. 7 78.0 32 1 hr. at 3,000 F. 2, 400 39. 7 26. 4 3, 000 18. 0 17. 8 58TBM-12, T-111+0.02N 320 187. 2 178. 3 25 Material reduced recrystallized112. 2 105. 7 29 1 hr. at 2,000 F. 2, 400 58. 0 41. 9 14 3,000 18. 9 18.4 43 TBM-18, T-l11+0.05N 320 224. 9 225. 2 18 Material reduced 75%;recrystallized 75 133. 8 132. 3 20 1 hr. at 3,000 F. 2, 400 56. 5 36. 324 3, 000 TBM-15, 'l111+0.01C+0.010+0.01N 320 188. 8 186.0 24 Materialreduced 70%; recrystallized 75 117.3 115.0 25 1 hr. at 3,000 F. 2, 40055. 0 37.9 45 3, 000 19.7 19. 5 122 Low Interstitial, T-lll, Pa-34 320147. 5 13 .0 31 Material reduced recrystallized 75 84.0 68. 6 31 1 hr.at 3,000 F. 2,400 38.0 26. 4 29 3, 000 15. 6 14. 5 31 Strain rate 0.005in./in.lmin at low temperatures. Strain rate 0.05 in./in./min. at hightemperatures.

ERTIES OF INTERSTITIAL-CONTAINING TANTALUINI ALLOYS AT 2400 F.

Stress for 1 Hr. Stress for 10 Hr.

Material Rupture Lite Rupture Life (K s.i.) (K s.i.)

Ta8W2Hf, Low Interstitial 5 26.

+0.01 C+0.01 O+0.0l N 40.0 30. 5

Interstitial amounts of carbon and nitrogen have a pronounced effect onrupture stress for One and ten hour rupture life. On the other hand,oxygen additions do not particularly benefit the stress ruptureproperties.

The addition of carbon and nitrogen to 0.02 w./o. either individually orin combination does not adversely affect the fabricability orweldability of the ternary alloy Ta8W2Hf, while producing a significantimprovement in tensile and stress rupture properties. In certainapplications, the addition of either carbon or nitrogen alone in amountsabove 0.02% and up to 0.05 w./o. results in improved properties.

The following examples are illustrative of the manner of preparingalloys disclosed by the present inventiornln these examples, thepercentages given for the composition are by weight (w./o.) and thehardness values are diamond pyramid hardness (d.p.h.).

EXAMPLE I An alloy of the following composition was prepared bynon-consumable arc melting: 86% tantalum, 11.2% tungsten and 2.8%hafnium. The resulting ingot was reduced 70% into sheet and samples ofthe sheet were recrystallized by heating for one hour at 3000 F. Whentested at a temperature of 3000 F., the ultimate tensile strength andthe 0.2% offset yield strength were both 20,100 p.s.i. and the resultingelongation was 38%. The samples had an average hardness of 240 d.p.h. inthe cast condition and 230 d.p.h. after reduction to sheet and annealingat 1 hr./3000 F.

EXAMPLE II An ingot of three inches diameter of an alloy of thefollowing composition was prepared by non-consumable arc melting: 88%tantalum, 9.6% tungsten, and 2.4 hafnium (nominal). Interstitial carbonin an amount of 0.011% was added. The ingot heated to 2200 F, was brokendown by high energy forging. This forged alloy has been found to exhibita 0.2% offset yield strength of 15,800 p.s.i. and an ultimate strengthof 15,900 p.s.i. at 3500 F., with an elongation of 37%. Sheets 6 inchesby 24 inches were produced from the foregoing by cold rolling. Thesamples had an average hardness of 292 d.p.h. in the as cast conditionand 286 d.p.h. after reduction to sheet and 1 hr. anneal at 3000 F. Thisexample illustrates the beneficial effect of the small amount of carbon.

Both single and double arc melting using consumable arc melting wereemployed to produce other ingots. The double arc melted ingot gavebetter results on high ternperature (3000 F. and over) tests, thoughboth were essentially similar in 2400 F. tests.

EXAM PLE l l l.

An alloy of the following composition was prepared by non-consumable arcmelting: tantalum, 8% tungsten and 2% hafnium. In addition, aninterstitial amount, 0.02% of nitrogen was introduced in the form of amaster alloy. Samples Were removed from the resulting ingot after it wasreduced 70% and recrystallized for one hour at 3000 F. The alloyexhibited an ultimate tensile strength of 18,900 p.s.i. and a 0.2%offset yield strength of 18,400 p.s.i. at 3000 F. with an elongation of43%. In addition, the alloy exhibited an excellent sub-zero at 320 F.ultimate tensile strength of 187,200 p.s.i., elongation of 25%, and a0.2% offset yield strength of 178,300 p.s.i. The average hardness of thesamples has been found to be 285 d.p.h. in the as cast condition and 270d.p.h. after reduction to sheet and annealing 1 hr. at 3000 F. Therupture strength of this alloy was found to be 43,500 p.s.i. and 32,500p.s.i. for one hour and ten hours stress rupture lives respectively.

Sheets and other members of the alloys of these xamples were readily cutinto desired shapes by machining, and were weldable into assemblies.

Small amounts of zirconium, preferably not exceeding /2% by weight, maybe present in the alloys of this invention. In amounts substantiallyabove /z%, the zirconium raises the weld bend transition temperature andinduces hot tearing during welding. If the alloy members are not to bewelded, then the alloy may include up to a maximum of 2% of zirconium.

It Will be understood that the foregoing description is only exemplaryand not limitative of the invention.

Accordingly what is claimed as new is:

1. A tantalum base alloy consisting essentially of tantalum, tungstenand hafnium, wherein the total tungsten and hafnium content of saidalloy ranges between 10% and 14%, from 0.005% to 0.05% carbon, from0.005% to 0.07% nitrogen and up to 0.07% oxygen, up to 0.5% zirconium,and the balance being tantalum except for small amounts of incidentalimpurities and wherein the ratio of tungsten to hafnium varies between2.5 :1 and 5.5 :1.

2. A tantalum base alloy consisting essentially of tantalum, tungstenand hafnium, wherein the total tungsten and hafnium content rangesbetween 12 and 14% by weight, from 0.005 to 0.5% carbon, from 0.005% to0.07% nitrogen and up to 0.07% oxygen, and the balance being tantalumexcept for small amounts of incidental impurities and wherein the ratioof tungsten to hafnium ranges between 2.5:1 and 5.5: 1.

3. A tantalum base alloy consisting essentially of tantalum, tungstenand hafnium, wherein the total tungsten and hafnium content rangesbetween 10 and 14% by weight, from 0.005% to 0.05% carbon and 0.005% to0.07% nitrogen, and up to 0.07% oxygen and the balance tantalum exceptfor incidental impurities and wherein the ratio of tungsten to hafniumranges between 3:1 and 5:1.

4. A tantalum base alloy consisting essentially of tantalum, tungstenand hafnium, wherein the total tungsten and hafnium content rangesbetween 10% and 14%, from 0.005% to 0.05% carbon, from 0.005% to 0.07%nitrogen and up to 0.07% oxygen, and the balance being tantalum exceptfor small amounts of incidental impurities wherein the ratio of tungstento hafnium is about 4:1.

5. A tantalum base alloy consisting essentially of tantalum, tungstenand hafnium, wherein the total tungsten and hafnium content rangesbetween 10% and 14%, from 0.01 to 0.05% by weight of at least one of thegroup consisting of carbon and nitrogen, up to 0.5% zirconium, and thebalance tantalum, the ratio of tungsten to hafnium being from 2.5:1 to5.5: 1.

6. A tantalum base alloy consisting essentially of tantalum, tungstenand hafnium, wherein the total tungsten and hafnium content rangesbetween 10 and 14% and wherein the ratio of tungsten to hafnium rangesbetween 2.5:l and 5.5: 1, and the balance tantalum, and from 0.01

to 0.05% by weight of at least one of the group consisting of carbon andnitrogen.

7. A tantalum base alloy consisting essentially of tantalum, tungstenand hafnium, wherein the total tungsten and hafnium content rangesbetween 10 and 14% and wherein the ratio of tungsten to hafnium rangesbetween 2.5:-1 and 5.511, and the balance tantalum and from 0.01 to0.05% by weight of carbon.

8. A tantalum base alloy consisting essentially of tantalum, tungstenand hafnium, wherein the total tungsten and hafnium content rangesbetween 10 and 14% and wherein the ratio of tungsten to hafnium rangesbetween 2.5 :1 and 55:1, and the balance tantalum and from 0.01 to 0.05by weight of nitrogen.

9. A tantalum base alloy consisting essentially of tantalum, tungstenand hafnium wherein the total tungsten and hafnium content rangesbetween 10 and 14% by weight and wherein the ratio of tungsten tohafnium is about 4:1 with the balance being tantalum, together with 10from 0.005 to 0.05% by weight of at least one of .the group consistingof carbon and nitrogen.

References Cited UNITED STATES PATENTS 3,243,290 3/1966 Clark et a1.75-174 3,113,863 12/1963 Chang et a1 75174 3,166,414 1/1965 France etal. 75174 OTHER REFERENCES Columbium-Base Alloys, General ElectricCompany, February 1962.

Temperature Dependence of the Tensile Properties of Tantalum, Pugh,Transactions of ASM, vol. 48, pp. 677 688.

CHARLES N. LOVELL, Primary Examiner.

DAVID L. RECK, Examiner.

1. A TANTALUM BASE ALLOY CONSISTING ESSENTIALLY OF TANTALUM, TUNGSTENAND HALNIUM, WHEREIN THE TOTAL TUNGSTEN AND HAFNIUM CONTENT OF SAIDALLOY RANGES BETWEEN 10% AND 14%, FROM 0.005% TO 0.05% CARBON, FROM0.005% TO 0.07% NITROGEN AND UP TO 0.07% OXYGEN, UP TO 0.5% ZIRCONIUM,AND THE BALANCE BEING TANTALUM EXCEPT FOR SMALL AMOUNTS OF INCIDENTALIMPURITIES AND WHEREIN THE RATIO OF TUNGSTEN OF HAFNIUM VARIES BETWEEN2.5:1 AND 5.5:1.